1. Field of the Invention
This invention relates to a finisher, which is connected to an image forming apparatus such as a printer or a copying machine, giving such additional-workings as sorting, binding, creasing, folding, and punching to a recording medium (hereinafter referred to briefly as "sheet") such as a recording paper outputted from the image forming apparatus. More particularly, it relates to a finisher with a folding device in which a stopper comes in contact with the leading end of the sheet to forms a loop and a pair of rollers nips the loop to fold the sheet.
2. Description of the Prior Art
Recently, various finishers have been proposed which give various additional-workings to a sheet with an image formed surface which are outputted from such image forming devices as printers and copying machines, (U.S. patent application Ser. No. 08/821,444). The term "additional-workings" as used herein means various working processes such as sorting sheets according to the number of copies, stapling sheets, folding sheets in two (hereinafter referred to as "double-folding"), folding sheets in three or in a cross section like a letter Z (hereinafter referred to as "Z-folding"), and punching sheets for filing.
In the field of conventional finishers, a folding device drives a leading end regulating device to contact the leading end of an incoming sheet to form a loop of the sheet and actuates a pair of folding rollers to nip the loop to fold the sheet.
The folding device can fold a sheet at a desired position by an adjustment of position of the leading-end regulating device relative to the folding rollers. Specifically, the folding device has a well-known mechanism, which automatically moves the leading-end regulating device into a conveying path located at a position which depends on a size of sheet and a mode of folding inputted by a user.
Known systems may include a drive unit such as a motor moves a single sheet or devices such as a solenoid to move sheet, and a method that devices as a solenoid move leading-end regulating devices, which are disposed at prescribed positions respectively, into and out of a conveying path to adjust the foremost position of the leading-end regulating device.
The former system has a problem of accuracy in positioning of the leading-end regulating device and does not always obtain the same position for regulating the leading-end of the sheet. The latter system requires many devices such as solenoids where a large number of regulating positions are prepared for regulating the leading-end of the sheet and thus, has a problem of boosting cost and rendering it difficult to attain a compact construction.